package com.lagou.sqlSession;

import com.lagou.config.BoundSql;
import com.lagou.pojo.Configuration;
import com.lagou.pojo.MappedStatement;
import com.lagou.utils.GenericTokenParser;
import com.lagou.utils.ParameterMapping;
import com.lagou.utils.ParameterMappingTokenHandler;

import java.beans.IntrospectionException;
import java.beans.PropertyDescriptor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;

/**
 * @author buddy
 * @date 2021/8/25
 */
public class SimpleExecutor implements Executor {


    @Override
    public <E> List<E> query(Configuration configuration, MappedStatement mappedStatement, Object... params) {
        try {
            // 1. 注册驱动，获取连接
            Connection connection = configuration.getDataSource().getConnection();
            // 2. 获取sql 语句:
            //      select * from user where id = #{id} and username = #{username}
            //      转换sql 语句
            //      select * from user where id = ? and username = ?
            String sql = mappedStatement.getSql();
            BoundSql boundSql = getBoundSql(sql);

            // 3. 获取预处理对象 preparedStatement
            PreparedStatement preparedStatement = connection.prepareStatement(boundSql.getSqlText());

            // 4. 设置参数
            // 获取到了参数的全路径
            String parameterType = mappedStatement.getParameterType();
            Class<?> parameterClass = getClassType(parameterType);
            List<ParameterMapping> parameterMappingList = boundSql.getParameterMappingList();
            for (int i = 0; i < parameterMappingList.size(); i++) {
                ParameterMapping parameterMapping = parameterMappingList.get(i);
                String parameterName = parameterMapping.getContent();
                // 反射
                Field declaredField = parameterClass.getDeclaredField(parameterName);
                // 暴力访问
                declaredField.setAccessible(true);
                // todo 为什么是 params[0] ？
                Object o = declaredField.get(params[0]);
                preparedStatement.setObject(i + 1, o);
            }

            // 5. 执行sql
            ResultSet resultSet = preparedStatement.executeQuery();

            // 6. 封装返回结果集
            String resultType = mappedStatement.getResultType();
            Class<?> resultClass = getClassType(resultType);
            List<Object> resultList = new ArrayList<>();
            while (resultSet.next()) {
                Object o = resultClass.newInstance();
                ResultSetMetaData metaData = resultSet.getMetaData();
                // todo 为什么从1开始？
                for (int i = 1; i <= metaData.getColumnCount(); i++) {
                    // 字段名
                    String columnName = metaData.getColumnName(i);
                    // 字段值
                    Object value = resultSet.getObject(columnName);
                    // 使用反射或者类型，根据数据库表和实体类的对应关系，完成封装
                    PropertyDescriptor propertyDescriptor = new PropertyDescriptor(columnName, resultClass);
                    Method writeMethod = propertyDescriptor.getWriteMethod();
                    writeMethod.invoke(o, value);
                }
                resultList.add(o);
            }
            return (List<E>) resultList;

        } catch (SQLException | NoSuchFieldException |
                IllegalAccessException | IntrospectionException
                | InstantiationException | InvocationTargetException exception) {
            exception.printStackTrace();
        }
        return null;
    }

    private Class<?> getClassType(String classPath) {
        if (classPath != null) {
            try {
                return Class.forName(classPath);
            } catch (ClassNotFoundException e) {
                e.printStackTrace();
            }
        }
        return null;
    }

    /**
     * 1. 完成对 #{} 的解析工作，将 #{} 使用 ? 进行代替
     * 2. 解析出 #{} 中的值进行存储
     *
     * @param sql
     * @return
     */
    private BoundSql getBoundSql(String sql) {

        // 标记处理类：配合标记解析器完成对占位符的解析处理工作
        ParameterMappingTokenHandler parameterMappingTokenHandler = new ParameterMappingTokenHandler();
        GenericTokenParser genericTokenParser = new GenericTokenParser("#{", "}", parameterMappingTokenHandler);
        // 解析出来的 sql
        String parseSql = genericTokenParser.parse(sql);
        // #{} 里面解析出来的参数名称
        List<ParameterMapping> parameterMappingList = parameterMappingTokenHandler.getParameterMappings();
        return new BoundSql(parseSql, parameterMappingList);
    }
}
